The invention relates to laser surgery apparatus, and in particular the invention is concerned with an improved laser beam delivery system for a surgical laser, wherein scanning and positioning the beam to points having transverse (X, Y) coordinates on the surgical target is accomplished more accurately and more efficiently.
Typically a surgical laser beam delivery system, to be manipulated in transverse directions along target tissue, i.e. in "X" and "Y" directions, must have some form of mechanical scanning component or components, usually behind an objective lens assembly. In most cases this function has been addressed by an internal mirror which is tiltable along two orthogonal rotational axes, under the control of servo motors. See, for example, copending U.S. patent application Ser. No. 475,657, filed Feb. 6, 1990 and assigned to the same assignee as the present invention.
Tilting mirrors can introduce inaccuracy into a surgical laser beam delivery system. A tilting mirror is secured at several mounting points and in addition is under the control of two different servo motors or galvo motors with linkages connecting to the mirror. With such a number of linkage components and points of mounting to base structure, there is a great potential for unwanted free movement or parts wear, and resulting inaccuracy in the tilt direction of the mirror. However, precision can be extremely important, particularly in eye surgery.
Another problem with the typical tilting mirrors is that they are normally positioned as close as practical to--but necessarily still a considerable distance from--the objective lens assembly of the system. This gives a longer lever arm for the tilted axis of the laser beam during scanning, resulting in either loss of some of the beam volume at the objective lens, or the need for a larger objective lens assembly to accommodate the swinging movements of the beam during scanning or positioning.
Further, the response time of a tilting mirror beam steering system, because of the relatively high moment of inertia thereof, can be somewhat slow and not always accurate for high speed ophthalmic surgery systems.
It is an object of the present invention described below to overcome these disadvantages and to provide an improved, more efficient and more accurate laser beam steering system.